No, they didn't want secession - they had built an army, and prepared transportation of that army as a hostile force against the Republic. And NO-ONE is endorsing slavery - in fact lets cut to the chase on this one. You are trying to find the Jedi guilty of flawed ethics based upon their use of a slave army. The reason that NOBODY EVER mentions this in the movies is because Lucas never gave it a second thought. It is a false paradigm by which to judge what the movies are telling us about the Jedi because it is a non-issue within the movies; because Lucas never addressed it; because Lucas never gave it a second thought. They have a huge army which manages to inflict immense damage on the galaxy. Their intention (which is obvious enough by what is discovered in itself - ie a huge droid army built in secret with an unusual concentration of Trade Federation ships....what do you think is going on?) is not secession but invasion of Republic planets. Their intention is to force the Republic to do things their way. And, just in case the physical evidence were not enough to discern that, Obi-Wan (and we the viewers) overhear Dooku and the Separatist leadership spell exactly that plan out.